Introduction to Mechanical Engineering: Machine Elements and Power Transmission Devices

1. Dr. DYPIEMR, AKURDI Unit 1 Introduction to Mechanical Engineering Mr. SiddharthShete

2. Unit 1. Introduction to Mechanical Engineering Syllabus Part A: Mechanical Elements Function, sketch, description and uses of shaft, axle, key (parallel key), coupling, (rigid flange), bearing (ball), clutch (single plate clutch), brake Part B: Power transmission devices Construction, working, comparison and applications of: Belt drive (flat and V-belt), chain drive and spur gear drive arranged with simple gear train.

3. Part AMechanical Elements Syllabus Function, sketch, description and uses of shaft, axle, key (parallel key), coupling, (rigid flange), bearing (ball), clutch (single plate clutch), brake

4. Introduction to machine • Device consisting of various elements arranged together so as to perform the prescribed task to satisfy human needs. • Examples- pump set, I.C. engine, turbine, screw jack, C-clamp etc. Input (source of energy) Machine (arrangement of elements) Output (prescribed task)

5. Introduction to machine elements • It is individual part or component of a machine which performs specific task. • Functions of machine elements are holding, supporting, transforming. • Types of machine elements • Holding- Nuts and bolts, cotters, rivets, clamps etc. • Supporting- Axle, bearing, brackets, body or frameetc. • Power transmitting- shafts, pulleys, belts, sprocket, chains, gears etc. Machine E4 E1 E2 E3

6. Shafts • Rotating member usually of circular C/S used to transmit power or motion. • For this purpose, various rotating members such as gears, pulleys, sprockets etc. are mounted on it. Fig. Shaft • Types of shafts • Transmission shaft • Machine shaft

7. Types of shafts F • Transmission shaft Fig. Transmission shaft • Used to transmit power between the source and the machines absorbing power. • They carry machine elements like pulleys, gears, flywheels, etc. • These shafts are subjected to bending and torsional moment. G M G Machine

8. Types of shafts 2. Machine shafts Fig. machine shaft (drilling machine spindle) • They form an integral part of the machine itself. • They are also subjected to bending and torsional moment. • For example: Cam-shaft, crankshaft, machine spindle, etc. Spindle Drill

9. Axle • An axle is a non-rotating or stationary machine element which carries no torque. • It is used to support the rotating machine elements like pulleys, brake drum, wheels, etc. • Though it is similar to shaft, it does not transmit torque; but it is subjected to bending moment only. Axle Whee l

10. Comparison between shaft and axle

11. KEYS • A key is the piece inserted in a axial direction between a shaft and hub to prevent relative rotation but allow sliding movement along the shaft if required. • Keys are temporary fastening and are always made of mild steel because they are subjected to shearing and compressive stresses caused by the torque they transmit. • a keyway is the groove cut in the shaft or hub to accommodate a key. Key ways can be milled horizontally or vertically .

12. KEYS Defination: The key can be defined as a machine element which is used to connect the transmission shaft to rotating elements like pulleys, gears, sprockets or flywheels. Functions: • To prevent the relative motion between the shaft and the hub of rotating element like : gear, pulley, or sprocket. • To transmit the torque from the shaft to the rotating element or vice-versa. • The selection of the type of key for a given application depends upon the following factors: • Power to be transmitted • Tightness of fit • Stability of connection • Cost

13. Types of keys • Saddle keys • Hollow saddle key • Flat saddle key • Sunk keys • Taper sunk keys • Parallel sunk keys • Feather keys • Woodruff key (adjustable key) • Round keys • Parallel pin • Taper pin • Tangent keys • Splines Taper sunk key Taper sunk key Gib-headed key Woodruff key

18. A round key is a straight pin of circular cross-section, fitted into a common hole drilled at the interface of shaft and hub Applications : Round keys and taper pins are commonly used for low power drives. Kennedy keys consist of two tapered square keys placed 90 apart. Applications : Kennedy keys are used in heavy duty industrial applications. A taper pin is a pin of circular cross-section, fitted into a common hole drilled through the hub and shaft, which is perpendicular to the axis of the shaft.

19. COUPLING • Coupling is the mechanical elementused to connect two shafts of a transmission systemandtransmit the torque from one shaft to another. Shaft 2 (driven) Shaft 1 (driving) Fig. Coupling

20. Functions of Coupling • It connects the shafts of two different units such as an electric motor and machine. • It introduces mechanical flexibility between two connected units and tolerates small misalignment between the connecting shafts. • It reduces the transmission of vibrations and shocks between two connected units.

21. Requirements of good coupling • It should transmit the full power from one shaft to another. • It should keep the shafts in perfect alignment. • It should absorb the slight misalignment that may be present between the driver and drive shaft. • It should be easy to connect and disconnect. • It should have no projecting parts.

22. Types of Couplings • Rigid coupling • Muff or sleeve coupling • Split muff or clamp coupling • Flange coupling • Flexible Coupling • Bushed-pin type • Universal or Hooke's • Oldham’s coupling Bushed-pin type

23. Types of couplings • Universal coupling • Oldham's coupling

24. Rigid Couplings • Rigid couplings are used to connect two shafts which are perfectly aligned. • These couplings are not capable of tolerating any misalignment between two shafts. • These couplings arenot capable of absorbing shocks and vibrations. • These are simple and inexpensive.

25. Protected type rigid flange coupling • It consists of two flanges: • one keyed to the driving shaft and other to the driven shaft. One of the flange has projected portion and other has a corresponding recess.This helps to bring two shafts in line and maintain the alignment. • The two flanges are coupled together by means of bolts and nuts. The number of bolts used are generally three, four or six. The two keys are staggered at right angles along the circumference of the shafts. • The flanges are made of cast iron, cast steel, or steel. • The torque is transmitted from the driving shaft to the left side flange through the key. It is then transmitted from the left side flange to the right side flange through the bolts. Finally, it is transmitted from the right side flange to the driven shaft through the key. • Advantages • The flange coupling is easy to assemble and disassemble. • It has high torque transmitting capacity. • Disadvantages • The flange coupling cannot tolerate misalignment between driving and driven shafts. • It requires more radial space. • Applications • The flange coupling is used for connecting electric motor to pump or compressor.

26. Protected type rigid flange coupling

27. Bearings • Bearing is a machine element which supports another moving machine element called as journal. • It permits a relative motion between the contact surfaces of the members. • Due to relative motion between the contact surfaces, there is friction and wear hence lubricant is required. • The commonly used lubricants are vegetable oil, silicon oil, grease, etc. Bearing

28. Function of a Bearing • The main function of a rotating shaft is to transmit power from one end of the line to the other. • It needs a good support to ensure stability and frictionless rotation. The support for the shaft is known as “bearing”. • The shaft has a “running fit” in a bearing. All bearing are provided some lubrication arrangement to reduced friction between shaft and bearing. • It also sustains the forces acting on the shaft or axle and transmits them to the frame of the machine.

29. Bearings are classified under two main categories: • Plain or slider bearing : - • In which the rotating shaft has a sliding contact with the bearing which is held stationary . Due to large contact area friction between mating parts is high requiring greater lubrication. • Rolling or anti-friction bearing : - • Due to less contact area rolling friction is much lesser than the sliding friction , hence these bearings are also known as antifriction bearing.

30. Rolling contact bearing- Ball bearing • Major parts: • Outer race • Inner race • Rolling element • Separator or retainer

31. Types of ball bearings • Single row deep-groove ball bearings • Double row deep-groove ball bearings • Angular contact bearings • Self-aligning bearings

32. Roller bearing

33. Clutches • Clutch is a mechanism to transmit rotary motion from one shaft (driving shaft) to another coincident shaft, (driven shaft), as and when required, without stopping the driver shaft. • Clutches are also required to disengage the drive from engine to gearbox for changing the gears. • During slowing of vehicle or stopping, the clutch is used to disengage engine from drive wheels and enable smooth stopping of vehicle. • Since clutch is of friction material, it also takes care of speed and torque variation from engine crankshaft to gearbox input shaft.

34. Functions of the clutch • When clutch is engaged (clutch pedal position-up), the clutch transmits maximum power from engine crankshaft to gearbox input shaft. • When clutch is disengaged (clutch pedal position-down), the clutch allows driver to shift the transmission in various gear positions (first, second, third, etc.) • When clutch is engaging (clutch pedal position-moving up), the clutch accommodates for minor slippages and hence provides smooth drive transmission without jerks.

35. Types of Clutches • Friction clutches • These clutches work on the friction principle that when two independent disc have relative motion between them, friction is caused. • Friction clutches are the most commonly used clutches. 2.Positive clutches • These clutches are used when positive drive is required. • These type of clutches are used in sprocket wheels, gears, pulleys, etc.

36. Single Plate Clutch • Single plate is the most commonly used type of clutch on automobiles. • It provides quicker disengagement. • It consists of clutch disc, pressure plate, and a cover assembly which are bolted to the engine flywheel.

37. Single plate clutch • Major components • Flywheel • Friction plate • Pressure plate • Thrust spring • Release lever • Clutch cover • Clutch shaft • Thrust bearing

38. Advantages & Disadvantages Advantages : • Simple design of construction and working. • Better heat dissipation from single plate. • Gear changing with single plate clutch is easier. • It has better torsional vibration absorbing capacity. Disadvantages : • For higher power transmission, the surface area of clutch plate increases and thereby increasing the overall size of clutch. • Clutch pedal force required is higher.

39. Brakes • Brake is a device with the help of which artificial frictional resistance is applied to a moving machine member, in order to stop or retard the motion of a machine. • While performing this function, the brake absorbs either kinetic energy of the moving member or potential energy given by objects being lowered by cranes, elevators, etc. • The energy absorbed by the brake is dissipated in the form of heat in the surrounding air, so that excessive heating of the brake lining does not take place.

40. Types of brakes Block brakes Disc brakes Band brakes Internal or external shoe brake

41. Disc Brake • Disc brakes are more efficient and now-a-days being adopted on large scale in the automotive segment. • It consists of a rotating brake disc mounted on the wheel and two friction pads positioned on either side of the disc. • The pressing of the stationary brake pads on the revolving disc causes friction, resulting in braking.

43. Advantages & Disadvantages Advantages : • The operation and assembly of disc brake is much simpler. • As the friction pads are flat, the wear and tear is uniform. • Heat dissipation is faster. Disadvantages : • The overall system cost is higher due to hydraulic caliper and fluid lines. • The frictional area of pads is less, thereby requiring high pressure intensity fluid.

44. Part BPower transmission devices Syllabus Construction, working, comparison and applications of: Belt drive (flat and V-belt), chain drive and spur gear drive arranged with simple gear train.

45. Introduction • Usually power is transmitted by means of belts, ropes, chains and gears. • For large distances, belt, ropes and chains are used and for smaller distances, gears are used. • Belts, ropes and chains are flexible type of connectors. • Owing to slipping and straining action, belts and ropes are not positive drive. • On the other hand, chains and gears are positive drives (rigid).

46. Belt drives • It consists of 3 elements: • Driving or head pulley • Driven or tail pulley • Endless belt • Power is transmitted because of frictional grip. Belt drive • Speed ratio of belt drive: • speed ratio = speed of driving pulley/speed of driven pulley • = n/N • = D/d • = (D+t)/(d+t) • Where, n and N = speed of driving and driven pulley in RPM • d and D = diameters of driving and driven pulleys in mm • t = thickness of belt in mm.

47. Types of belts • Materials used for belts • Leather • Cotton • Rubber

48. Comparison between flat and V-belt

49. Types of flat belt drives Open belt with idler pulley drive Open belt drive Compound belt drive Crossed belt drive

50. Advantages and disadvantages of belt drive • Advantages • Can be used for long Centre distances • Absorb shocks and vibrations • Lubrication is not required • Not affected due to dirt and dust • Do not require precise alignment of shaft and pulley • Disadvantages • Low power transmitting capacity • Can not be used at extremely high speeds • Shorter life and more space as compared to gear drive • Not positive drive